In liquid crystal projectors and DLP projectors such as data projectors and projectors for home theaters which are required to be small in the size and provide bright projection images, short arc type high pressure mercury vapor discharge lamps small in the size and capable of obtaining lighting at high luminosity have been used as light source apparatus therefor. However, since the high pressure discharge lamps of this type involve a problem that the starting performance during a cold condition and re-starting performance upon hot restrike are not generally favorable. Therefore, it is necessary to provide means for enhancing the starting performance. However, since a space is not available for allowing location of a starting auxiliary electrode, etc. that promotes arc discharge between electrodes upon start of ignition to be disposed in the discharge bulb of a small-sized lamp, the lamp voltage upon starting the high-pressure discharge lamp has been set to a somewhat higher level and a starting voltage such as a high frequency voltage or a high frequency pulse voltage has been applied to promote arc discharge between the electrodes.
However, when the voltage of the high frequency pulse applied between the electrodes is increased in order to enhance the starting performance of the high-pressure discharge lamp, since the voltage leak has to be prevented by extending the insulation distance between wirings forming a lighting circuit of the lamp, this not only results in a problem that the size of the lighting circuit is increased and the size of the liquid crystal projector cannot be decreased, as well as it may possibly generate noises which cause erroneous operation to electronic circuits etc. of the liquid crystal projector.
Then, in a high-pressure discharge lamp 51A shown in FIG. 7, for starting ignition by high frequency pulses at a relatively low voltage, a metal wire 53 referred to as a trigger wire/antenna wire is disposed outside of an arc tube 52 for promoting discharge between electrodes 56 and 56. That is, the lamp tube 51A is a short arc type high voltage mercury vapor discharge lamp in which a pair of tungsten electrodes 56 and 56 are opposed each other at a short inter-electrode distance of about 1 mm in a discharge bulb 54 of an arc tube 52 comprising a quartz glass tube, mercury and a starting gas comprising a halogen such as bromine and an argon gas are sealed, a pair of electrode seal portions 59R and 59L are formed by airtightly sealing portions from the discharge bulb 54 to both ends of the arc tube 52 by means of shrinking seal to seal electrodes 56, metal foils 57, and electrode leads 58 of electrode assemblies 55 inserted through both ends thereof, and connected to a lighting circuit by way of the electrode leads 58 and 58 protruded from the ends of each of the electrode seal portions 59R, 59L. The metal wire 53 for enhancing the starting performance of the lamp is connected at one end 53a to an electrode lead 58 that protrudes from the end of the electrode seal portion 58R on one side of the arc tube 52 and wound around at the other end 53b in a loop-form or a spiral-form around the outer periphery of the electrode seal portion 59L on the other side of the arc tube 52 (refer to Patent documents 1 to 4).
When the metal wire 53 is wired in close contact with or approximate to the surface of the arc tube 52, the starting performance of the lamp 51A is enhanced more. However, this results in a problem that the re-starting performance upon hot re-strike is not favorable since the wire is extended due to thermal expansion by being heated at a high temperature of about 900° C. to 1000° C. upon lighting of the lamp and recedes from the surface of the arc tube 52. Further, since the metal wire 53 is entirely slackened or distorted by the generation of extension due to thermal expansion, it tends to recede from the surface of the arc tube 52, as well as the once slackened or distorted metal wire 53 does not restore the initial state where it was in close contact with or approximate to the surface of the arc tube 52 even when the wire is cooled and thermally shrank after distinguishing the lamp, the starting performance during cold condition is also deteriorated.
[Patent document 1] JP-A No. 2004-335457
[Patent document 2] JP-A No. 9-265947
[Patent document 3] JP-A No. 8-87984
[Patent document 4] Re-laid open publication No. 2004-90934
Then, a high pressure discharge lamp 51B shown in a plan view of FIG. 8(a) and in a fragmentary enlarged cross sectional view of FIG. 8(b) is configurated such that when electrode seal portions 59R and 59L are formed by shrink sealing both ends of an arc tube 52, a cavity 60 for containing a portion of a metal foil 57 is formed in one electrode seal portion 59L and, at the same time, fabrication of sealing a rare gas such as an argon gas containing mercury vapor in the cavity 60 is applied, one end of a metal wire 53 connected at other end to an electrode lead 58 that protrudes from the end face of the electrode seal portion 59R is wound around the outer periphery of the electrode seal portion 59L having the cavity 60 formed therein, whereby high frequency pulse voltage is applied between the metal wire 53 and the metal foil 57 contained in the cavity 60 of the electrode seal portion 59L to cause grow discharge in the mercury vapor in the cavity 60. The mercury is excited by the glow discharge to generate a UV-light, which excites the starting gas sealed in a discharge bulb 54 to promote arc discharge between the electrodes 56 and 56 (refer to Patent document 5).
However, since it is extremely troublesome to apply fabrication of forming the cavity 60 in the electrode seal portion 59L of the arc tube 52 and seal a mercury vapor-containing rare gas in the cavity 60 in the course of manufacturing the high pressure discharge lamp 51B, and the amount of mercury and the volume, gas pressure, etc. of the rare gas to be sealed in the cavity 60 have to be controlled properly in order to generate a necessary amount of a UV-light by glow discharge, the fabrication is troublesome and may remarkably lower the lamp productivity. Further, when the cavity 60 is formed in the electrode seal portion 59L of the arc tube 52, the mechanical strength of the electrode seal portion 59L is lowered to possibly cause breakage of the arc tube 52.
Further, during lighting of the high pressure discharge lamp, since the atmospheric temperature in a concave reflector to which the lamp is attached generally rises to a high temperature of 300° C. or higher in average, the mercury vapor pressure in the cavity 60 increases excessively in the high pressure discharge lamp 51B shown in FIG. 8 under the effect of such high temperature. Therefore, even when a high frequency pulse voltage for starting is applied between the metal foil 57 and the metal wire 53, since the mercury vapor pressure in the cavity 60 remains excessively high for a while after extinguishing the lamp and the glow discharge is not caused. Glow discharge can be obtained only after the atmospheric temperature in the concave reflector is lowered to about 100° C. in average. Accordingly, the high pressure discharge lamp 51B involves a problem that the re-starting performance is not favorable during hot strike of re-ignition just after the lamp is distinguished.
[Patent document 5] JP-T 2003-526182
Then, in a light source apparatus shown in FIG. 9, a high pressure discharge lamp 51C having substantially the same basic structure as that in the high pressure discharge lamp 51A shown in FIG. 7 is attached integrally with a reflector 61, by inserting an electrode seal portion 59L on one side through a bottom hole 62 apertured in the bottom of the concave reflector 61, and an ignition antenna 63 as a UV-enhancer that radiates a UV-light to a discharge bulb 54 for enhancing the starting performance of the lamp 51C upon ignition thereof is disposed in parallel with the optical axis of an arc tube 52 along the outer periphery of the electrode seal portion 59L (refer to Patent document 6).
The ignition antenna 63 has a configuration, as shown in an enlarged view of FIG. 10(a) and a cross sectional view along X-X in FIG. 10 (b) that an ionizing filler (mercury and argon gas) is filled in an antenna vessel 64 comprising a quartz glass tube having a long straight tube portion 65a extending along the electrode seal portion 59L to the vicinity of the discharge bulb 54 of the lamp 51C, and a bent tube portion 65b bent into a semi-arcuate shape so as to be wound around for 180° C. over the outer periphery of the electrode seal portion 59L at the top end of the long straight tube portion 65a, an electric conductor element 66 comprising a metal foil (molybdenum foil) is contained and disposed in the straight tube portion 65a on the side of the free end of the antenna vessel 64, and an external electrode 67 comprising a metal bush is fitted to the straight tube portion 65a on the side of the free end.
In the ignition antenna 63, a portion of an external electrode 67 is secured by a cement 68 to the outer periphery of the electrode seal portion 59L, and the external electrode 67 is connected by way of a current supply conductor 69 to the output portion of voltage transformer means 71 connected between current conductors 70R and 70L that form a lighting circuit of the high pressure discharge lamp 51C. When a starting voltage such as a high frequency AC voltage or a pulse voltage is applied between the external electrode 67 and the electric conductor element 66 in the antenna vessel 64, electric discharge is caused therebetween to generate a UV-light, and the UV-light is radiated by way of the straight tube portion 65a and the bent tube portion 65b of the antenna vessel 64 into the discharge bulb 54 of the lamp 51C thereby promoting arc discharge between the electrodes 56 and 56.
However, the antenna vessel 64 in which the straight tube portion 65A and the bent portion 65B are contiguous with each other is troublesome and involve a drawback of increasing the manufacturing cost. Further, since the antenna vessel 64 is adjacent at the bent tube portion 65b with the discharge bulb 54 of the lamp 51C which is heated to a high temperature of about 1000° C. upon lighting the lamp, discharge between the external electrode 67 and the electric conductor element 66 become instable just after distinguishing the lamp under the effect of the high temperature to result in a problem that the re-starting performance upon hot re-strike is not favorable and, at the same time, the antenna vessel 64 may be possibly broken undergoing thermal damages.
Further, there is also a disadvantage that the UV-light generated by discharge between the external electrode 67 and the electric conductor element 66 is decayed by being reflected, diffracted, or absorbed to the filler in the antenna vessel 64 in the course of passage byway of the long straight portion tube 65a and the bent tube portion 65b of the antenna vessel 64 into the discharge bulb 54 of the lamp 51C. Further, since the bent tube portion 65b of the antenna vessel 64 is disposed in adjacent with one side of the discharge bulb 54 of the lamp 51C, this may result in a disadvantage that the temperature distribution during lighting of the lamp is remarkably different between one side and the opposite side of the discharge bulb 54 of the lamp 51C which may possibly deteriorate the lamp life and that the bent tube portion 65b of the antenna vessel 64 shields a portion of alight emitted from the discharge bulb 54 of the lamp 51C to the bottom of the concave reflector 61 to lower the light utilization efficiency of the lamp. Further, there may be a possibility that the ignition antenna 63 is detached from the outer periphery of the electrode seal portion 59L due to the aging deterioration (thermal degradation) of a cement 68 that secures the ignition antenna 63 to the outer periphery of the electrode seal portion 59L.
[Patent document 6] JP-T 2003-523055
Then, the present applicant has proposed a light source apparatus as shown in FIG. 11 in which a glow discharge tube 80 that generates a UV-light upon starting lighting of a high pressure discharge lamp 51D is disposed at a position capable of radiating the UV-light from the outside of a concave reflector 81 through a vent hole 82 for cooling air formed in the reflector to the discharge bulb 54 of the lamp 51D (refer to Patent document 7).
In the light source apparatus in FIG. 11, a high pressure discharge lamp 51D having an identical basic structure with that of the high pressure discharge lamp 51A shown in FIG. 7 or the high pressure discharge lamp 51C shown in FIG. 9 is attached integrally with the reflector 81 by inserting a sealing portion 59L on one side through a bottom hole 83 apertured in the bottom of the concave reflector 81, and a glow discharge tube 80 as a UV-enhancer that radiates a UV-light for enhancing the starting performance upon starting lighting of the lamp 51D to the discharge bulb 54 is disposed outside of the reflector 82. Accordingly, the discharge tube 80 is not heated to a high temperature during lighting and the mercury vapor pressure inside the tube is not increased excessively and glow discharge can be caused to generate a UV-light also in the hot state just after distinguishing the lamp.
Further, the glow discharge lamp 80 has a simple structure in which a rare gas such as an argon gas containing mercury vapor is sealed inside a glass sealing tube 84 comprising quartz glass and an internal electrode 85 comprising a metal foil having a pair of lead wires 86 and 86 protruding from both ends of the glass sealing tube 84 are contained and disposed therein, and a coiled external electrode 87 formed by winding a chromium/aluminum/iron alloy wire 89 of about 0.2 mm diameter is disposed to the outer periphery of the glass sealing tube 84. Accordingly, this provides an advantage that the manufacturing cost is not increased.
Then, the internal electrode 85 and the external electrode 87 of the glow discharge tube 80 are connected to one side 88R and the other side 88L of the lamp lighting circuit, a high frequency pulse voltage for staring is applied between the internal electrode 85 and the external electrode 87, whereby glow discharge is caused in the mercury vapor in the glass sealing tube 84 as a main body of the discharge tube 80 to generate a UV-light, and a portion of the UV-light is radiated through a vent hole 82 for cooling air formed in the reflector 81 to the discharge bulb 54 of the lamp 51D disposed inside the reflector 81 directly or radiated after reflection on the reflection surface of the reflection mirror 81.
However, when the position for locating the discharge tube 80 is far from the vent hole 82 of the reflector 81, the amount of the UV-light radiated through the vent hole 82 to the inside of the reflector 81 is decreased to result in a problem of lowering the starting performance of the lamp. On the other hand, when the discharge tube 80 is disposed in adjacent with the vent hole 82 in the reflector 81, since the discharge tube 80 closes the vent hole 82 to hinder the flow of the cooling air, this results in a problem of lowering the cooling effect for the lamp 52D.
Further, when the number of turns of the coils of the coiled external electrode 87 disposed to the outer periphery of the discharge tube 80 is small, since the amount of the UV-light to be generated is small, a necessary and sufficient amount of the UV rays cannot be radiated into the discharge bulb 54 of the lamp 51D. On the other hand, when the number of turns of the coils of the coiled external electrode 87 is increased, the UV-light is shielded by the external electrode 87 to result in a problem that a necessary and sufficient amount of the UV-light cannot be radiated into the discharge bulb 54 of the lamp 51D.
[Patent document 7] Registered Utility Model No. 3137961